Numerical simulation of the charge balance in an EBIT

The electron beam ions traps (EBITs) are widely used to study highly charged ions (HCIs). In an EBIT, a high energy electron beam collides with atoms and ions to generate HCIs in the trap region. It is important to study the physics in the trap. The atomic processes, such as electron impact ionisation (EI), radiative recombination (RR), dielectronic recombination (DR) and charge exchange (CX), occur in the trap and numerical simulation can give some parameters for design, predict the composition and describe charge state evolution in an EBIT [Phys. Rev. A 43 (199 1) 4861]. We are presently developing a new code, which additionally includes a description of the overlaps between the ion clouds of the various charge-states. It has been written so that it can simulate experiments where various machine parameters (e.g. beam energy and current) can vary throughout the simulation and will be able to use cross- sections either based on scaling laws or derived from atomic structure calculations. An object-oriented method is used in developing the new software, which is an efficient way to organize and write code. (C) 2003 Elsevier Science B.V. All rights reserved.

A new device for the study of electron-ion interactions: The Belfast EBIT

An electron beam ion trap ( EBIT) has been designed and is currently under construction for use in atomic physics experiments at the Queen's University, Belfast. In contrast to traditional EBITs where pairs of superconducting magnets are used, a pair of permanent magnets will be used to compress the electron beam. The permanent magnets have been designed in conjunction with bespoke vacuum ports to give unprecedented access for photon detection. Furthermore, the bespoke vacuum ports facillitate a versatile, reconfigurable trap structure able to accommodate various in-situ detectors and in-line charged particle analysers. Although the machine will have somewhat lower specifications than many existing EBITs in terms of beam current density, it is hoped that the unique features will facilitate a number of hitherto impossible studies involving interactions between electrons and highly charged ions. In this article the new machine's design is outlined along with some suggestions of the type of process to be studied once the construction is completed.

Experimental investigation of the processes determining x-ray emission intensities from charge-exchange collisions

Absolute cross sections have been measured for single and double charge exchange and x-ray line emission for highly charged ions of C, N, 0, and Ne colliding with He, H-2 CO2, and H2O at collisions energies of 7q keV. Present results of charge exchange in He and H-2 compare favorably with previous results. For CO2 and H2O, where prior work is scarce, the classical overbarrier model is found to overestimate results by up to a factor of 3. An analysis of the relative intensities of the observed Lyman x-ray transitions indicates that capture into l states is not statistical, as collision velocities are insufficient to populate the highest angular-momentum states. The importance of autoionization following multiple capture is highlighted, and enhanced radiative stabilization following double capture is observed and compared to other studies. Present results are also discussed in terms of mechanisms likely to generate x-ray emission in comets.

Investigation of resonant inner-shell processes with an electron beam ion trap

The collision processes of highly charged ions with electrons have been studied with an electron beam ion trap. Resonant inner-shell processes such as dielectronic recombination and resonant excitation double autoionization were investigated by observing the number ratio of extracted ions with adjacent charge states. (c) 2006 Elsevier Ltd. All rights reserved.

Injection of metallic elements into an electron-beam ion trap using a Knudsen cell

A method of injecting metallic elements into an electron-beam ion trap (EBIT) is described. The method is advantageous over the conventional coaxial and pulsed injection methods in two ways: (a) complicated switching of injection and extraction beams can be avoided when extracting beams of highly charged ions from the EBIT and (b) a beam of stable intensity can be achieved. This method may be applicable to any metallic elements or metallic compounds that have vapor pressures of similar to 0.1 Pa at a temperature lower than 1900 degrees C. We have employed this method for the extraction of highly charged ions of Bi, Er, Fe, and Ho. (c) 2006 American Institute of Physics.

Effective collision strengths for transitions of Ni XVII

Electron impact excitation collision strengths are required for the analysis and interpretation of stellar observations. This calculation aims to provide fine structure effective collision strengths for the Ni XVII ion using a method which includes contributions from resonances. A DARC calculation has been performed, involving 37 J pi states. The effective collision strengths are calculated by averaging the electron collision strengths over a Maxwellian distribution of electron velocities. The non-zero effective collision strengths for transitions between the fine structure levels are given for electron temperatures (T(e)) in the range log(10) T(e)(K) = 4.5 - 8.5. Data for several transitions from the ground state are discussed in this paper.

Characterization and parametrization in terms of atomic number of x-ray emission from K-shell filling during ion-surface interactions

When highly charged ions are incident on a surface, part of their potential energy is emitted as characteristic radiation. The energies and yields of these characteristic x rays have been measured for a series of elements at the Tokyo electron-beam ion trap. These data have been used to develop a simple model of the relaxation of the hollow atoms which are formed as the ion approaches the surface, as well as a set of semiempirical scaling laws, which allow for the ready calculation of the K-shell x-ray spectrum which would be produced by an arbitrary slow bare or hydrogenlike ion on a surface. These semiempirical scaling laws can be used to assess the merit of highly charged ion fluorescence x-ray generation in a wide range of applications.